Case Study: Air Traffic Control Radar Survelillance System

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1a) Air Traffic Control radar surveillance system
Air traffic control (ATC) is a service provided by ground-based controllers who direct aircraft on the ground and in the air. The purpose of ATC systems worldwide is to separate aircraft to prevent collisions, to organize and expedite the flow of traffic, and to provide information and other support for pilots when able.

b) The operating principles of ATC radar survelliance system
Primary Radar
Principle:
The primary radar unit has a major quality: It works with passive echoes. The transmitted high-frequency impulses are reflected by the target and then received by the same radar unit. Direct cause of the reflected echo is the transmitting impulse sent out by the radar unit.

Secondary Radar
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Ground stations alternates the two types of interrogations, and send them quickly enough so that the transponder receives several of each on each sweep of the radar antenna. The airborne transponder measures The space between P1 and P3 of the received signal and determines the type of request, Mode A or Mode C.For instance if the P1-P3 timing is 8 microseconds, a Mode A response is expected, and if 21 microseconds, the request is for Mode C data.
As the directional antenna transmits the interrogation signal, the signals often leaks through the sides of the antenna.This is call ‘sidelob signals’ Aircrafts flying close to the antenna will respond to the sidelobe signals, causing interference on the channel.
Hence , an additional pulse is used to provide additional information to the receiving aircraft. The interrogation signal now consists of two pulses, P1 and P2. The directional antenna firsts sents P1 followed omnidirectional antenna which will send P2. When the aircrafts receives the signal, P1 is significantly stronger than P2. Airborne Transponders receiving signals will compare the first two pulses in the transmission, and reply only if P1 was significantly stronger than P2. When P1 approximately equal to P2. The transponder will be temporarily disabled, for 35 microseconds, preventing the aircrafts from responding to the sidelob signals. A Mode S data signal
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Computer processor
The computer processor contains the hardware and software that connects all components of the TCAS. Radar signals are transmitted by the processor through the antennas. This signals measures range ,altitude of nearby traffic, watches for other incoming aircrafts and computes escape paths when there is a conflict. These information are then sent to the cockpit displays and indicators.
Directional antennas
The antennas are mounted on top and bottom of the aircraft’s fuselage. They are needed for cockpit traffic displays and reducing radar interference.
TCAS Cockpit Display
The TCAS cockpit indicators displays range approximate bearing, altitude of other approaching aircrafts that is equipped a mode s transponder. TCAS also alerts the crew with visual and aural traffic advisory to any intruding aircraft at 40sec of closest approach.
Mode S transponder
Relays data between aircrafts during air traffic. Facilitates identity and flight status and altitude of

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